Android ProgrammingReading “The Big Nerd Ranch Guide” Bruce Tsai

Activity States

Resumed (Running)

Paused

Stopped

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Activity LifecycleBack? Home?

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Back StackIntact Last in, first out

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Multitasks

Task is cohesive unit that can move to “background” when user begins a new task or go to Home screen

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Start Other ActivityVia ActivityManager

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Intent

Object that component uses to communicate with OS

Explicit intent — start activities within application

create Intent with Context and Class

Implicit intent — start activities in another application

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Intent i = new Intent(QuizActivity.this, CheatActivity.class);!

startActivity(i);

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Put Intent Extras (parent)

Intent i = new Intent(QuizActivity.this, CheatActivity.class);!

i.putExtra(CheatActivity.EXTRA_ANSWER_IS_TRUE, true);!

startActivity(i);

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Use Intent Extra (child)mAnswerIsTrue = getIntent().getBooleanExtra(EXTRA_ANSWER_IS_TRUE, false);

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Get Activity Result

Intent i = new Intent(QuizActivity.this, CheatActivity.class);!

i.putExtra(CheatActivity.EXTRA_ANSWER_IS_TRUE, true);!

startActivity(i);!

startActivityForResult(i, 0);

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Set Result (child)Intent data = new Intent();!

data.putExtra(EXTRA_ANSWER_SHOWN, true);!

setResult(RESULT_OK, data);

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Handle Result (parent)protected void onActivityResult(int requestCode, int resultCode, Intent data) {!

! if (data == null) return;!

! mIsCheater = !data.getBooleanExtra(CheatActivity.EXTRA_ANSWER_SHOWN, false);!

}

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FragmentController object that activity can deputize to perform tasks

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Support LibraryFragment is introduced from API level 11

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Fragment HostActivity defines a spot in its layout for fragment’s view

Activity manage lifecycle of fragment instance

Hosting approaches: add to layout or add to code

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Fragment Manager

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Fragment Transaction

Usages of fragment in activities are add, remove, replace and perform other actions

Each set of changes that is committed to activity is fragment transaction

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FragmentManager fm = getSupportFragmentManager();!

Fragment fragment = fm.findFragmentById(R.id.fragmentContainer);!

if (fragment == null) {!

! fragment = new CrimeFragment();!

! fm.beginTransaction()! .add(R.id.fragmentContainer)! .commit();!

}

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SDK Versions

Minimum SDK version — hard floor below which the OS should refuse to install the app

Target SDK version — API level the app is designed to run on

Build SDK version — private information between you and compiler

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dp (dip) — density-independent pixel

sp — scale-independent pixel

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<Button ! android:layout_width=“wrap_content”! android:layout_weight=“1” />!

<CheckBox ! android:layout_width=“wrap_content”! android:layout_weight=“1” />